ADP5023 Analog Devices, ADP5023 Datasheet - Page 15

• Manufacturer Part Number: ADP5023
• Description: Dual 3 MHz, 800 mA Buck Regulator with One 300 mA LDO
• Manufacturer: Analog Devices

Data Sheet
POWER DISSIPATION AND THERMAL CONSIDERATIONS
The
the power dissipated in the device is not a concern. However,
if the device operates at high ambient temperatures and maxi-
mum loading condition, the junction temperature can reach
the maximum allowable operating limit (125°C).
When the temperature exceeds 150°C, the
all the regulators, allowing the device to cool down. When the
die temperature falls below 130°C, the
normal operation.
This section provides guidelines to calculate the power dissi-
pated in the device and ensure that the
below the maximum allowable junction temperature.
The efficiency for each regulator on the
where:
η is the efficiency.
P
P
Power loss is given by
or
Power dissipation can be calculated in several ways. The most
intuitive and practical is to measure the power dissipated at the
input and all the outputs. Perform the measurements at the
worst-case conditions (voltages, currents, and temperature).
The difference between input and output power is dissipated in
the device and the inductor. Use Equation 4 to derive the power
lost in the inductor, and from this use Equation 3 to calculate
the power dissipation in the
A second method to estimate the power dissipation uses the
efficiency curves provided for the buck regulator, and the power
lost on the LDO can be calculated using Equation 12. When the
buck efficiency is known, use Equation 2b to derive the total
power lost in the buck regulator and inductor, use Equation 4 to
derive the power lost in the inductor, and then calculate the
power dissipation in the buck converter using Equation 3. Add
the power dissipated in the buck and in the LDO to find the
total dissipated power.
Note that the buck efficiency curves are typical values and may
not be provided for all possible combinations of V
I
safety margin when calculating the power dissipated in the buck.
A third way to estimate the power dissipation is analytical and
involves modeling the losses in the buck circuit provided by
Equation 8 to Equation 11 and the losses in the LDO provided
by Equation 12.
OUT
IN
OUT
is the input power.
. To account for these variations, it is necessary to include a
ADP5023
P
P
η
is the output power.
LOSS
LOSS
=
P
= P
= P
P
OUT
IN
IN
OUT
×
is a highly efficient µPMU, and, in most cases,
− P
100%
(1− η)/η
OUT
ADP5023
ADP5023
buck converter.
ADP5023
ADP5023
ADP5023
resumes
operates
IN
is given by
, V
turns off
OUT
, and
(2b)
(2a)
Rev. A | Page 15 of 28
(1)
BUCK REGULATOR POWER DISSIPATION
The power loss of the buck regulator is approximated by
where:
P
regulators.
P
The inductor losses are external to the device and do not have
any effect on the die temperature.
The inductor losses are estimated (without core losses) by
where:
DCR
I
where r is the normalized inductor ripple current
where:
L is the inductance.
f
D is the duty cycle.
ADP5023
power switch conductive losses, the switch losses, and the transi-
tion losses of each channel. There are other sources of loss, but
these are generally less significant at high output load currents,
where the thermal limit of the application is. Equation 8
captures the calculation that must be made to estimate the
power dissipation in the buck regulator.
The power switch conductive losses are due to the output current,
I
power switches that have internal resistance, RDS
RDS
where RDS
mately 0.16 Ω at 125°C junction temperature and VIN1 = VIN2 =
3.6 V. At VIN1 = VIN2 = 2.3 V, these values change to 0.31 Ω and
0.21 Ω, respectively, and at VIN1 = VIN2 = 5.5 V, the values are
0.16 Ω and 0.14 Ω, respectively.
SW
OUT1(RMS)
OUT1
DBUCK
L
is the inductor power losses.
is the switching frequency.
, flowing through the P-MOSFET and the N-MOSFET
ON-N
P
P
r = V
D = V
P
P
L
I
LOSS
L
is the inductor series resistance.
DBUCK
COND
OUT
is the power dissipation on one of the
≈ I
. The amount of conductive power loss is found by
is the rms load current of the buck regulator.
( 1
= P
OUT1
OUT1(RMS)
buck regulator power dissipation, P
OUT1
= [RDS
RMS
ON-P
= P
DBUCK
)
× (1 − D)/(I
/V
COND
is approximately 0.2 Ω, and RDS
=
IN1
I
2
ON-P
OUT1
+ P
× DCR
+ P
L
× D + RDS
SW
×
+ P
L
OUT1
1
+
TRAN
12
× L × f
r
ON-N
SW
× (1 − D)] × I
)
ADP5023
DBUCK
ON-N
ON-P
ADP5023
OUT1
, includes the
is approxi-
and
2
buck
(3)
(4)
(5)
(6)
(7)
(8)
(9)